1. Field of the Invention
The present invention relates to image processing and, more particularly, to systems for editing digital images.
2. Background of the Technology
A large number of applications require combining one video image with another video image, i.e., a television broadcast of a weather person in front of weather maps during a weather report, so as to produce a composite video image. One well-known technique for producing composite video images is commonly referred to as "chroma-key". The chroma-key technique is so named because it uses the chroma or color information portion of a television signal as a "key" to control the formation of a composite image. A chroma-key device is essentially a video multiplexer which selects a video input signal by feeding the chroma signal from one of the two video inputs to decision logic.
In the case of the above-mentioned weather report application, a television camera is directed at a weather reporter standing in front of a vertical sheet, called a matte, which has a predetermined blue hue or color shade. Hue is the dimension of color that is referred to a scale of perceptions ranging from red through yellow, green, and blue, and circularly back to red. The image of the weather reporter and matte foreground source is provided to the chroma-key device, which is programmed to select all of the video signals received from the camera, except those video signals that represent portions of the image having the predetermined blue hue. Thus, the chroma-key device effectively separates the image of the reporter from the image of the matte.
At the same time that the previously described operation takes place, a video image of a weather map or satellite view of the earth, either of which may be superimposed with city names, high/low temperatures, and the like, is provided to the chroma-key device as a background source. The decision logic of the chroma key device selects the background source as video output wherever a blue hue is detected in the foreground source and presents the resulting background and foreground as a composite picture on a studio monitor that can be viewed by the reporter. The reporter can then point to positions on the matte that correspond to geographic locations on the background source and the viewer of the television program sees a composite image of a reporter and a weather map. Such a composite image is the desired output of a chroma-key device.
However, as was noted in U.S. Pat. No. 4,811,084 to Belmares-Sarabia, et al., a major disadvantage of a chromakey system is that false keys can be produced. For example, weather reporters wearing blue or striped suits, and even blue eyes, may cause a chroma-key system to produce an incorrectly spliced composite. Also, a chroma-key device is used too large a distance between the reporter and the matte causing reflections resulting from false keying, hence restraining the movements of the reporter.
To overcome the problems inherent in chroma-keying, the Belmares-Sarabia, et al., patent discusses a device for video color detection that does not depend on a single color for keying. For example, such a device is also said to discriminate among similar hues by limiting the bandwidth of the hues and/or hue and saturation combinations that can be recognized by the device.
The device disclosed in Belmares-Sarabia, et al., uses an analog process to multiplex television signals. Analog processes, however, are not as versatile in combining images as are digital processes, which can be programmed to apply sophisticated image processing algorithms to a digitized image so as to alter or edit an image. Thus, it would be an advancement in the technology to provide a digital image editing system which can strip a digital image of an object from a background and combine the digital object with a different digital background or backgrounds (composite) without suffering from the above-mentioned problems and limitations.
Other ways of producing a composite image include image editing software programs running on a Macintosh.RTM. computer available from Apple Computer, Inc., or a PC type compatible computer available from IBM and other companies. These programs are exemplified by Picture Publisher.RTM. produced by Micrografx, Inc. for the PC and Adobe Photoshop.TM. produced by Adobe Systems Incorporated for the Macintosh. Picture Publisher is a registered trademark of Micrografx, Inc. Adobe Photoshop is a trademark of Adobe Systems Incorporated. Macintosh is a registered trademark of Apple Computer, Inc.
These programs enable the user to place one object image in front of a background scene and to cut and remove the object image. However, these programs are limited to working with one object only. These programs cannot build a set of layers of objects and backgrounds and allow the user to move an object to different depths or layers into the composite image. In other words, a person could not be placed behind a fence but in front of a house of the background scene simultaneously. Thus, it would be an advancement in technology to provide a system which could place an object in front or behind any other object or the background at any desired depth into the composite image. It would also be desirable to make part of an object which was moved into a particular layer to be transparent based on a desired attribute of the object. For example, one attribute of the object is hue, which is the perceived color shade. The leaves of a tree, which have a particular hue range of green, could be set to be transparent rather than opaque. Thus, the sky would then be seen between the branches of the tree, wherein previously, the leaves had blocked the sky.
When producing a composite image involving the face of a person, one may desire to remove the original person's face and replace it with the face of another person. Frequently the two faces will not be the same size, e.g., one face is a closeup and the other is not, and the person trying to make the composite image will have to reduce or enlarge the replacement face to fit. This may involve numerous trials to achieve a pleasing appearance. Thus, it would be desirable to provide a system which can automatically size the replacement face to provide a natural appearance without a trial and error process.
Another aspect to consider when replacing one face for another is the coloration of the skin. The person making the composite image may be placing a fair complexioned face to replace a dark complexioned face. The rest of the body, such as hands, arms and legs, may be visible in the original image. The composite would therefore not appear natural after the replacement was done. Thus, it would be desirable to provide a system which can automatically match the skin tone of the replacement face to that of the original face without any manual intervention to provide a natural appearance for the resultant composite image.
A further aspect to consider when replacing one face for another in creating a composite image is the positioning of the replacement face. This positioning may involve an iterative process to try different placements to achieve a pleasing and natural appearance. Thus, it would be desirable to provide a system which can automatically position the replacement face at the appropriate location to produce a pleasing appearance for the resultant composite image.
It is often the case that an object is imaged under one lighting condition and is then overlaid on a background that was imaged under another lighting condition. Consequently, the composite image may look artificial. Thus, it would be a further advantage if the editing system could establish the same lighting conditions, or "gamma" for the entire composite image. For example, it may be desirable to have an object that was imaged under fluorescent light inserted into a background that was imaged under full daylight and have the composite image maintain the same lighting condition. The lighting condition of the composite image could even be a third condition such as moonlight.
Accordingly, a need exists to provide a digital image editing system which can separate the digital image of an object from a background against which the object was imaged. It is a further purpose of the present invention to provide a digital image editing system which can automatically size, position, and layer the digital image of a replacement object or multiple objects into a predetermined background at a desired depth, and then match the lighting conditions of the replacement object with one or more original objects and the background, and to provide a digital image editing system that is easy to implement and cost-effective to use.